The long term goal of the proposed research is to identify on the molecular and cellular levels ion transport proteins that mediate salt transport across the corneal endothelium and to relate their properties to the deturgesing function of this cell layer. The immediate goals of this research program are to characterize K+ channels in the bovine corneal endothelium in terms of their molecular and biophysical properties, determine their cellular distribution, and assess their role in endothelial cell ionic homeostasis and transendothelial HCO3- transport. Potassium channels play a pivotal role in the regulation of transendothelial salt transport because the maintenance of cell ionic composition requires that K+ efflux be coupled in an obligatory fashion to the activity of the Na+ pump. Recently, the applicant and his colleagues have identified a homolog of the inwardly rectifying K+ channel (IRK1) in corneal endothelial cells and have shown the presence of IRK-like channel activity by patch clamp assays. The specific aims of the proposed research are to: 1) clone and sequence the bovine corneal endothelial IRK1 homolog, BCE-IRK; 2) determine the expression and localization of BCE-IRK in the endothelial cells; 3) characterize the biophysical properties of the BCE-IRK in a heterologous expression system; 4) compare the properties of K+ channels identified in corneal endothelial cells with those of BCE-IRK; and 5) explore regulation of K+ channels in a cell culture model for corneal endothelial hypertrophy.